For a virtual display device, two positive lenses are arranged in front of a display panel in such a manner that a focal length of each positive lens is greater than a distance between the display panel and the positive lens. In this way, the positive lens functions as a magnifying lens capable of magnifying an image and enabling the image farther from a human eye. Hence, erected virtual images acquired at a near-to-eye position through the positive lenses may be combined in a brain, so as to produce a stereo image.
The conventional virtual display device has the following drawbacks. The two positive lenses are relatively thick and heavy. In addition, an optical aberration may occur due to the single lens, and thereby a feeling of discomfort may occur when the virtual display device is worn by a person or the image is displayed on the virtual display device. Further, the virtual image displayed by the virtual display device has a fixed spatial depth.